Hi Bluey27,
Welcome to the forums!
I can't really comment on bio and legal because I haven't done it, but I did do maths advanced, modern, and history extension.
On maths, I'm currently studying computer science in uni and I can say that maths will be super helpful if you're thinking of doing any further study in science, engineering, or even adjacent fields like economics and finance. A lot of the social sciences like history can also make use of maths for things like data analysis, so I would personally recommend keeping advanced even if it's a bit boring, simply because it's so foundational to many fields. If it's any consolation, maths gets more interesting once you get to uni because you can start to see how it applies to your field if you do end up doing further study.
I really enjoyed modern in year 11, and History Extension ended up being my overall favorite subject for the HSC, so I'm naturally biased in saying you should take it if in any way possible. The content is super interesting in that instead of studying any particular event, you study how history is constructed and the field of history itself, focusing on prominent historians and historical debates. You also get to do a major project and formulate your own research on anything you want - I did mine on how Twitter has impacted historical debates, and other people in my class did projects on everything from Hamilton and musical theater to the representation of egyptian pharaohs. It's a heavy course, but in a good way in that it will challenge your views of history and make you a much better historian for your other history subjects as well. I personally think this is one of the best courses the HSC offers, so take that as you will.
Hope this helps, lmk if you have any other questions about this